Apparatus for variably adjusting the control times of gas exchange valves in an internal combustion engine

ABSTRACT

An apparatus for variably adjusting control times of gas exchange valves in an internal combustion engine. The apparatus has a driving element, an output element, at least one pressure chamber, a pressurized medium supply device, and at least one pressure accumulator. The supply device allows pressurized medium to be fed to or discharged from the pressure chamber. A phase angle of the output element relative to the input element can be changed by feeding or discharging pressurized medium to or from the pressure chamber. The pressure accumulator encompasses a movable element that has a first pressure surface which partially delimits a storage space. The storage space is or can be connected to the supply device. An energy store applies a force to the movable element in the direction of an initial position. The movable element can be moved against the force of the energy store by pressurizing the storage space.

FIELD OF THE INVENTION

The invention relates to a device for variably adjusting the controltimes of gas exchange valves of an internal combustion engine, having adrive input element, a drive output element, at least one pressurechamber, a pressure medium supply device and at least one pressureaccumulator, with it being possible for pressure medium to be suppliedto or discharged from the at least one pressure chamber by means of thepressure medium supply device, with it being possible for a phaseposition of the drive output element relative to the drive input elementto be varied by means of the supply of pressure medium to or dischargeof pressure medium out of the pressure chamber, with the pressureaccumulator having a movable element which is provided with a firstpressure surface which partially delimits a store chamber, with thestore chamber being connected or being connectable to the pressuremedium supply device, with a force store loading the movable elementwith a force in the direction of an initial position, and with it beingpossible by means of the pressurization of a the store chamber for themovable element to be moved counter to the force of the force store.

BACKGROUND OF THE INVENTION

In modern internal combustion engines, use is made of devices forvariably adjusting the control times of gas exchange valves in order tobe able to make the phase relationship between the crankshaft andcamshaft variable in a defined angle range between a maximum earlyposition and a maximum late position. The device conventionallycomprises an actuating device which is driven by a crankshaft and whichtransmits the torque of said crankshaft to the camshaft. Here, theactuating device has formed within it a hydraulic actuating drive whichmakes it possible to targetedly influence the phase position between thecrankshaft and camshaft. A pressure medium supply device is provided forsupplying pressure medium to the actuating device.

A device of said type is known for example from EP 1 025 343 B1. Thedevice comprises two rotors which are rotatable relative to one another,with an outer rotor being drive-connected to the crankshaft and with theinner rotor being rotationally fixedly connected to the camshaft. Thedevice comprises a plurality of cavities, with each of the cavitiesbeing divided by means of a vane into two oppositely-acting pressurechambers. By supplying pressure medium to and discharging pressuremedium from the pressure chambers, the vanes are moved within thepressure chambers, thereby effecting a targeted rotation of the rotorsrelative to one another, and therefore of the camshaft relative to thecrankshaft.

The pressure medium supply to the pressure chambers and the pressuremedium discharge from the pressure chambers is controlled by means of apressure medium supply device which comprises a pressure medium pump, atank, a control valve and a plurality of pressure medium lines. Here, apressure medium line connects the pressure medium pump to the controlvalve. In each case one further pressure medium line connects one of theworking ports of the control valve to the pressure chambers. Thepressure medium is conventionally extracted from the lubricant circuitof the internal combustion engine.

To ensure the function of the device, the pressure in the pressuremedium system must exceed a certain value in all operating phases of theinternal combustion engine. This is particularly critical in the idlerunning phases of the internal combustion engine, since the pressuremedium pump is driven by the crankshaft and therefore the systempressure rises with the rotational speed of the internal combustionengine. The system pressure provided by the pressure medium pump is alsodependent on the pressure medium temperature, with the system pressurefalling with rising temperature. The pressure medium pump must thereforebe designed so as to provide sufficient system pressure under the mostunfavorable conditions, in order to ensure a sufficiently fastadjustment of the phase position of the inner rotor relative to theouter rotor. To ensure the required adjusting speed even under the mostunfavorable pressure conditions, such as for example high pressuremedium temperatures and/or low rotational speeds, the pressure mediumpump must be designed accordingly. As a result, use is made of pressuremedium pumps which are designed for the peak demands of the actuatingdevice, and which are therefore of excessively large dimensions duringmost operating phases of the internal combustion engine. It isalternatively possible to use controllable pressure medium pumps whichprovide pressure medium according to demand. In both cases, theincreased expenditure has an adverse effect on the costs, theinstallation space requirement and the fuel consumption of the internalcombustion engine.

U.S. Pat. No. 5,775,279 A discloses a further device of said type. Insaid embodiment, a pressure accumulator is arranged between the pressuremedium pump and the control valve, which pressure accumulatorcommunicates with the pressure medium supply device. Said pressureaccumulator is filled with pressure medium in phases of high systempressure. When the system pressure falls, then the pressure accumulatoris emptied automatically, as a result of which additional pressuremedium is supplied to the pressure medium supply device. The phaseadjustment of the device is assisted in this way.

A disadvantage of said embodiment is the fact that the pressureaccumulator is emptied even if the system pressure falls not on accountof an adjustment process but rather on account of other externalcircumstances, for example as a result of a drop in the rotationalspeed. Therefore, reduced pressure assistance and a smaller pressuremedium volume from the pressure accumulator are available for asubsequent phase adjustment process.

A further disadvantage is that the maximum pressure with which thepressure accumulator can assist the pressure medium supply devicecorresponds to the pressure which prevailed in the pressure mediumsupply device directly before the phase adjustment process. When theengine controller transmits an adjustment demand to the device at hightemperatures and low rotational speeds, then the pressure assistancefrom the pressure accumulator is less pronounced, because the systempressure with which the pressure accumulator was filled was low. Thismay have the result that the adjustment process cannot be carried out,or that the adjustment speed is considerably reduced. It is thereforenecessary in this case, too, for the pressure medium pump to be designedfor the peak load, with the resulting disadvantages.

OBJECT OF THE INVENTION

The invention is based on the object of providing a device for variablyadjusting the control times of gas exchange valves of an internalcombustion engine, with it being sought to ensure a functionallyreliable adjustment of control times at high adjustment speeds in alloperating phases of the internal combustion engine. Here, it shouldlikewise be possible to dispense with an overdimensioning of thepressure medium pump (design for the expected peak loads), and with theuse of variable pressure medium pumps.

The object is achieved according to the invention in that the movableelement has a counterpressure surface which at least partially delimitsa counterpressure chamber, with it being possible by means of theapplication of pressure medium to the counterpressure chamber for themovable element to be moved in the direction of the initial position.

The movable element may for example be designed as a pressure pistonwhich can be moved within a pressure reservoir counter to the force of aforce store which is designed for example as a spring element. In theevent of a supply of pressure medium to the store chamber, the volume ofthe latter increases at the expense of the counterpressure chamber. Whenthe system pressure in the pressure medium supply device falls, then theforce of the force store exceeds the force on the first pressure surfacecaused by the system pressure. The pressure piston is thus pushed by theforce store into an initial position in which the volume of the storechamber is at a minimum.

As an alternative to the spring element, use may also be made of othertypes of force stores, for example reversibly deformable bodies, forexample composed of elastomers, or gas-filled balloons.

When the counterpressure chamber is acted on with pressure medium inthose operating phases of the internal combustion engine in which thepressure accumulator is to dispense pressure medium to the pressuremedium supply device, then the movable element is acted on not only bythe force of the force store but also by a further force which pushessaid movable element in the direction of the initial position. Saidadditional force results from the pressure in the counterpressurechamber, which acts on the counterpressure surface. The magnitude F ofsaid additional force can be defined as: F=pA_(G), where p is thepressure acting on the counterpressure surface and A_(G) is the surfacearea of the counterpressure surface.

As a result of the increase of the pressure provided by the pressureaccumulator, the pressure accumulator can accommodate peak consumptions,such that the pressure medium pump can be designed for the normaloperation of the internal combustion engine. No overdimensioned orcontrolled pressure medium pumps are required in order to ensure afunctionally reliable and fast adjustment of the phase position. Theadjustment speed of the actuating device is additionally increased.Alternatively, for the same adjustment speed, the actuating device maybe dimensioned to be smaller. The mass, mass moment of inertia and costscan be reduced in this way.

In one refinement of the invention, it may be provided that the movableelement have at least one second pressure surface which partiallydelimits a control chamber, with it being possible by means of thepressurization of the control chamber for the movable element to bemoved counter to the force of the force store, and with a pressuremedium flow within the pressure accumulator from the store chamber intothe control chamber being prevented. Furthermore, it may be providedthat the store chamber and the control chamber do not communicate withone another within the pressure accumulator. An application of pressuremedium to the store chamber advantageously moves the movable element inthe same direction as an application of pressure medium to the controlchamber, advantageously away from the initial position of the movableelement.

By forming the pressure accumulator with a movable element, whichpartially delimits pressure chambers, which are isolated from oneanother within the pressure accumulator, said two pressure chambers canbe activated, that is to say filled and/or emptied, separately from oneanother. Aside from leakage, there is no connection between the pressurechambers. It is thus possible, for example, to use different pressuresources for filling the store chamber and the control chamber.

It is alternatively also possible for a pressure medium connection to beprovided within the pressure accumulator between the store chamber andthe control chamber. Pressure medium which is supplied to the controlchamber can pass via said pressure medium connection into the storechamber. Here, however, it should be ensured that a reversed pressuremedium flow, from the store chamber into the control chamber, isprevented. This may be realized for example by means of a pressuremedium duct in the pressure piston or in the pressure reservoir of thepressure accumulator, in which pressure medium duct a check valve isarranged. In said case, the filling of the store chamber and of thecontrol chamber may take place solely by means of the filling of thecontrol chamber. When the pressure accumulator is to be emptied, thenthe control chamber is connected to the tank. The store chamber emptiesinto the pressure medium supply device, and the control chamber empties,unpressurized, into the tank. A passage of pressure medium from thestore chamber into the control chamber is prevented by the check valve.

If it is provided that an application of pressure medium to the storechamber moves the movable element in the same direction as anapplication of pressure medium to the control chamber, then the controlchamber can assist the filling of the store chamber. For this purpose,the control chamber is likewise filled with pressure medium during thefilling process of the store chamber. In this way, a force is exerted onboth pressure surfaces of the pressure piston, as a result of which ahigher force is stored in the force store (the spring element iscompressed to a greater extent). When the filled pressure accumulatorreceives the command from the engine controller to assist the phaseadjustment process, then the control chamber can be emptiedindependently of the store chamber. That is to say, while the storechamber is emptied into the pressure medium supply device and therebyassists the phase adjustment process, the control chamber can beventilated to atmospheric pressure into a tank. With suitable design,the ventilation of the control chamber can take place more quickly thanthe emptying of the store chamber into the pressure medium supplydevice. The entire force which has been stored in the force storetherefore acts on the store chamber via the first pressure surface. As aresult, the pressure at the start of the assistance process can increaseby a factor of:

$\frac{A_{1} + A_{2}}{A_{1}}$

as a function of the load acting on the force store at said time. Here,A₁ corresponds to the surface area of the first pressure surface and A₂corresponds to the surface area of the second pressure surface. If useis made, for example, of a spring element as a force store, then thepressure at the start of the assistance process is increased by the fullfactor

$\frac{A_{1} + A_{2}}{A_{1}}$

for as long as the spring has not yet reached its maximally compressedstate.

In one refinement of the invention, the counter-pressure chamber may beselectively connected to a pressure source or to a tank.

Control means may be provided, with it being possible for thecounterpressure chamber to be selectively connected to a tank or to apressure source by the control means.

Here, the counterpressure chamber may be connected to the pressuremedium pump of the internal combustion engine. The counterpressurechamber may be connected to the tank of the internal combustion engine.

The pressure source may for example be the pressure medium supply deviceor the pressure medium pump thereof, or a source separate from these,for example the pressure source of a servo consumer (for example theservo steering system). In the second case, it is possible for thepressure accumulator to be completely filled even in operating phaseswith low system pressure. The selective connection to a pressure sourceor to the tank is produced via control means, for example a 3/2directional valve in the form of a switching valve (for example seatvalve) or a proportional valve (for example slide valve). Considerationmay alternatively be given to two control means, with one of the controlmeans blocking or opening up the connection from the pressure source tothe counterpressure chamber and with the other control means blocking oropening up the connection from the counterpressure chamber to the tank.The control means may for example be electromagnetically actuatedhydraulic valves such as directional valves (for example switching orproportional valves), double check valves or the like. Said controlmeans receive control signals from an engine control unit of theinternal combustion engine, according to which control signals thecounterpressure chamber is filled or emptied, that is to say whether thepressure accumulator should be filled or the emptying process should beassisted.

It is likewise conceivable to use hydraulically actuated control means.Here, it may be provided that the hydraulic actuating device of thecontrol means communicates with the pressure medium supply device. Thecontrol means are thus automatically switched when the pressure in thepressure medium supply device falls below a defined value. Thisconsiderably reduces the regulating expenditure.

If the tank and/or the pressure medium pump of the internal combustionengine are/is used for filling and ventilating the counterpressurechamber, then no further components beyond those already present in theinternal combustion engine in any case are required. Furthermore, thedemands on the seal between the pressue medium reservoir and pressurepiston are lower, since a mixing of the pressure medium in the storechamber and in the counterpressure chamber is admissible. It istherefore possible to dispense with a sealing element which acts betweenthe pressure piston and the pressure reservoir.

Furthermore, it may be provided that a directional valve is provided asa control means, which directional valve has one port each connected tothe pressure source, the tank, and the counterpressure chamber. In adevelopment of the invention, a further port may be provided, which portis connected to the store chamber or the control chamber.

The pressure assistance of the pressure accumulator can thus beactivated by simply switching one or more control means. Here, thepressure medium volume is provided which is collected in the storechamber in those operating phases of the internal combustion engine inwhich the phase position is held constant.

The pressure assistance of the pressure accumulator can be utilizedduring every phase adjustment process. For this purpose, the controlmeans (directional valves and/or double check valves) are placed intothe position in which the store chamber is emptied whenever a phaseadjustment is demanded. In the operating phases between the phaseadjustment demands, the pressure accumulator can be filled.

A further possibility is for the pressure assistance of the pressureaccumulator to be activated according to demand. When the enginecontroller detects that the pressure or volume flow provided by thepressure medium pump is not sufficient for the phase adjustment, thensaid engine controller enables the pressure assistance by the pressureaccumulator. This approach lengthens the times in which the pressureaccumulator can be filled, and therefore the performance of the pressureaccumulator during the pressure assistance.

It may alternatively be provided that the pressure assistance of thepressure accumulator be utilized merely as a “boost” function forcritical adjustment processes which require for example a high volumeflow or a high adjustment speed. When the engine controller detects thata critical adjustment process of said type should be initiated, thensaid engine controller enables the pressure assistance by means ofsuitable setting of the control means.

It is likewise conceivable for the control means to be formed in onepiece with the control valve which controls the pressure medium flow toand from the pressure chambers of the actuating device.

The maximum volume of the store chamber advantageously corresponds to atleast two times the volume required for a phase adjustment from amaximum late position to a maximum early position.

The pressure accumulator may for example open out into the pressuremedium line between the pressure medium pump and the control valve.

It may alternatively be provided that the pressure accumulator open outinto one of the pressure medium lines which connects one of the workingports of the control valve to one group of pressure chambers. It isadditionally possible in said embodiment for a second pressureaccumulator to be provided which opens out into the pressure medium linewhich connects the other working port of the control valve to the othergroup of pressure chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention emerge from the following descriptionand from the drawings, which illustrate exemplary embodiments of theinvention in simplified form. In the drawings:

FIG. 1 shows an internal combustion engine in only highly schematicform;

FIG. 2 a shows a longitudinal section through the actuating device;

FIG. 2 b shows a cross section through an actuating device;

FIG. 3 shows a first embodiment of a device according to invention;

FIG. 4 shows a second embodiment of a device according to the invention;and

FIG. 5 shows a third embodiment of a device according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of an internal combustion engine 1, indicating apiston 3, which is seated on a crankshaft 2, in a cylinder 4. In theillustrated embodiment, the crankshaft 2 is connected to an inletcamshaft 6 and an outlet camshaft 7 via in each case one tractionmechanism drive 5, with it being possible for a relative rotationbetween the crankshaft 2 and the camshafts 6, 7 to be effected by meansof a first and a second device 10. The devices 10 comprise in each caseone hydraulic actuating device 10 a,b and a pressure medium supplydevice 37. Cams 8 of the camshafts 6, 7 actuate one or more inlet gasexchange valves 9 a or one or more outlet gas exchange valves 9 b,respectively. It is likewise possible for only one of the camshafts 6, 7to be equipped with a device 10, or for only one camshaft 6, 7 to beprovided, which is equipped with a device 10.

FIG. 3 shows a first embodiment of a device 10 according to theinvention, having actuating devices 10 a,b of a pressure medium supplydevice 37 and a pressure accumulator 43. FIGS. 2 a and 2 b show anactuating device 10 a,b in longitudinal section and in cross section,respectively.

The actuating device 10 a,b has a drive input element designed as anouter rotor 22 and a drive output element designed as an inner rotor 23.The outer rotor 22 has a housing 22 a and two side covers 24, 25 whichare arranged on the axial side surfaces of the housing 22 a. The innerrotor 23 is formed in the manner of an impeller and has a substantiallycylindrical hub element 26, from the outer cylindrical lateral surfaceof which five vanes 27 extend in the radially outward direction in theillustrated embodiment. The vanes 27 are formed separately from theinner rotor 23 and are arranged in vane grooves 28 which are formed onthe hub element 26. The vanes 27 are loaded in the radially outwarddirection with a force by means of vane springs 27 a which are arrangedbetween the groove bases of the vane grooves 28 and the vanes 27.

Proceeding from an outer circumferential wall 29 of the housing 22 a, aplurality of projections 30 extend in the radially inward direction. Inthe illustrated embodiment, the projections 30 are formed in one piecewith the circumferential wall 29. The outer rotor 22 is mounted on theinner rotor 23, so as to be rotatable relative thereto, by means ofradially inner circumferential walls of the projections 30.

A sprocket 21 is arranged on an outer lateral surface of thecircumferential wall 29, by means of which sprocket 21 torque istransmittable from the crankshaft 2 to the outer rotor 22 via a chaindrive (not illustrated).

In each case one of the side covers 24, 25 is arranged on one of theaxial side surfaces of the housing 22 a and rotationally fixedlyconnected to the latter. For this purpose, an axial opening is providedin each projection 30, through which axial opening extends a fasteningelement 32, for example a screw, which serves for rotationally fixedlyfastening the side cover 24, 25 to the housing 22 a.

Within the actuating device 10 a,b, a cavity 33 is formed between ineach case two projections 30 which are adjacent in the circumferentialdirection. Each of the cavities 33 is delimited in the circumferentialdirection by opposite, substantially radially extending delimiting walls34 of adjacent projections 30, in the axial direction by the side covers24, 25, in the radially inward direction by the hub element 26, and inthe radially outward direction by the circumferential wall 29. A vane 27projects into each of the cavities 33, with the vanes 27 being designedso as to bear both against the side covers 24, 25 and also against thecircumferential wall 29. Each vane 27 thereby divides the respectivecavity 33 into two oppositely acting pressure chambers 35, 36.

The inner rotor 23 is rotatable relative to the outer rotor 22 in adefined angle range. The angle range is limited in one rotationaldirection of the inner rotor 23 in that the vanes 27 come to bearagainst in each case one corresponding delimiting wall 34 (early stop 34a) of the cavities 33. Similarly, the angle range is delimited in theother rotational direction in that the vanes 27 come to bear against theother delimiting walls 34, which serve as a late stop 34 b, of thecavities 33.

The phase position of the outer rotor 22 relative to the inner rotor 23can be varied by pressurizing one group of pressure chambers 35, 36 andrelieving the other group of pressure. The phase position of the tworotors 22, 23 relative to one another can be held constant bypressurizing both groups of pressure chambers 35, 36. Alternatively, itmay be provided that none of the pressure chambers 35, 36 are acted onwith pressure medium during phases of constant phase position. Ashydraulic pressure medium, use is conventionally made of the lubricatingoil of the internal combustion engine 1.

To supply pressure medium to and discharge pressure medium from thepressure chambers 35, 36, a pressure medium supply device 37 is providedwhich is illustrated in FIG. 3. The pressure medium supply device 37comprises a pressure source, which is designed as a pressure medium pump38, a tank 39, a control valve 40 and a plurality of pressure mediumlines 41. The control valve 40 has an inlet port P, a tank port T andtwo working ports A, B. In each case one of the pressure medium lines 41connects the pressure medium pump 38 to the inlet port P, the firstworking port A to the first pressure chamber 35, the second working portB to the second pressure chamber 36, and the tank port T to the tank 39.Pressure medium can therefore pass from the pressure medium pump 38 tothe inlet port P of the control valve 40 via the pressure medium line41.

In a first position of the control valve 40, the inlet port P isconnected to the first pressure chambers 35, while the second pressurechambers 36 are connected to the tank 39.

In a second position of the control valve 40, it is provided that noneof the pressure chambers 35, 36 communicate with the tank 39 and theinlet port P.

In a third position of the control valve 40, the inlet port P isconnected to the second pressure chambers 36, while the first pressurechambers 35 are connected to the tank 39.

During the operation of the internal combustion engine 1, an alternatingtorque acts on the camshaft 6, 7, which alternating torque is caused bythe rolling of the cams 8 on cam followers. Here, the force of valvesprings acts on the camshaft 6, 7 with a braking action until the gasexchange valve is fully open. The camshaft 6, 7 is subsequentlyaccelerated by the force of the valve springs. Consequently, pressurepeaks are generated within the actuating device 10 a,b, which pressurepeaks cause the pressure chambers 35, 36 which are connected to theinlet port P to be emptied counter to the pressure medium pump 38, whichleads to a considerable reduction in the adjustment speed. To preventthis, a check valve 42 a is provided in the pressure medium line 41which connects the pressure medium pump 38 to the control valve 40. Thecheck valve 42 a prevents the pressure medium from flowing back from thepressure chambers 35, 36 to the pressure medium pump 38 via the controlvalve 40. The pressure peaks are supported on the check valve 42 a, as aresult of which an inadvertent emptying of the pressure chambers 35, 36is effectively prevented and the rigidity of the torque transmission andthe adjustment speed are increased.

The adjustment speed of the actuating devices 10 a,b is dependent on theprovided pressure or the provided pressure medium volume flow of thepressure medium pump 38. The provided pressure, or the provided pressuremedium volume flow, are in turn dependent on numerous factors, forexample the rotational speed of the internal combustion engine 1 and thepressure medium temperature. To ensure the demanded adjustment speedeven under the most unfavorable conditions, such as for example highpressure medium temperatures and/or low rotational speeds, the pressuremedium pump 38 must be designed accordingly. As a result, use is made ofpressure medium pumps 38 which are designed for the peak demands of theactuating device 10 a,b, and which are therefore of excessively largedimensions during most operating phases of the internal combustionengine 1. It is alternatively possible to use controllable pressuremedium pumps 38 which provide pressure medium according to demand. Inboth cases, the increased expenditure has an adverse effect on the costsand the fuel consumption of the internal combustion engine 1.

To avoid said disadvantages, a pressure accumulator 43 is provided inthe device 10 according to the invention. The pressure accumulator 43comprises a movable element which is designed as a pressure piston 45and which can be moved within a pressure reservoir 44 counter to theforce of a force store. In the illustrated embodiment, the force storeis designed as a spring element 46. However, other types of force store,such as, for example suitably shaped elastomer bodies or gas-filledballoons, are also conceivable.

The pressure piston 45 has two pressure surfaces 47, 48. Together withthe pressure reservoir 44, the first pressure surface 47 delimits astore chamber 49, with the first pressure surface 47 delimiting thestore chamber 49 in the movement direction of the pressure piston 45.The pressure reservoir 44 and the pressure piston 45 delimit a controlchamber 50, with the second pressure surface 48 delimiting the controlchamber 50 likewise in the movement direction of the pressure piston 45.Here, the pressure piston 45 and the pressure reservoir 44 are designedsuch that there is no connection between the two pressure chambers 49and 50 within the pressure accumulator 43. Aside from leakage, noexchange of pressure medium takes place between said pressure chambers49, 50 in this embodiment. In the illustrated embodiment, the pressuresurfaces 47, 48 are arranged offset relative to one another in themovement direction of the pressure piston 45, with the first pressuresurface 47 being surrounded by the second pressure surface 48 in theplane intersected perpendicularly by the movement direction of thepressure piston 45. The first pressure surface 47 is of circular designand the second pressure surface 48 is of annular design. By means of anapplication of pressure medium to the pressure chambers 49, 50, thepressure piston 45 is moved counter to the force of the spring element46, as a result of which the volume of the pressure chambers 49, 50increases. The distance by which the pressure piston 45 can be movedcounter to the spring element 46 is delimited by stops 54 formed withinthe pressure reservoir 44. The stops 54 are arranged such that aconnection of the store chamber 49 to the control chamber 50 isprevented.

The spring element 46 is supported at one side on that side of thepressure piston 45 which faces away from the pressure chambers 49, 50,and at the other side on that side of the pressure reservoir 44 whichfaces away from the pressure chambers 49, 50. Here, the spring element46 is mounted in the pressure accumulator 43 with preload, such that thevolume of the pressure chambers 49, 50 at low system pressure isminimal. In this initial position, the pressure piston 45 bears, at itsside facing away from the spring element 46, against the pressurereservoir 44.

That region of the pressure reservoir 44 which faces away from thepressure surfaces 47, 48 is designed as a pressure chamber(counterpressure chamber 58). Here, that surface of the pressure piston45 which faces toward the counterpressure chamber 58 acts as acounterpressure surface 59. By means of an application of pressuremedium to the counterpressure chamber 58, a force acts on the pressurepiston 45 via the counterpressure surface 59, which force is alignedparallel to the force of the spring element 46. In the illustratedembodiment, the counterpressure surface 59 is of planar design and isaligned perpendicular to the movement direction of the pressure piston45. It is likewise conceivable for inclined surfaces to be provided, orfor the counterpressure surface 59 to have further functional elementssuch that it differs from the planar form. For example, retainers forthe spring element 46 could be formed on the counterpressure surface 59.

The store chamber 49 is connected by means of a store line 51 to thepressure medium supply device 37. The store line 51 opens out on the onehand into the pressure medium supply device 37 downstream of the checkvalve 42 a and on the other hand via a port 56 into the store chamber49. A check valve 42 c is arranged in the store line, which check valve42 c permits a pressure medium flow from the store chamber 49 to thepressure medium supply device 37 and prevents a pressure medium flow inthe opposite direction. In this way, it is achieved that pressure peakswhich are generated in the actuating devices 10 a,b cannot penetrate tothe store chamber 49 of the pressure accumulator 43, but rather aresupported on the check valve 42 c. The hydraulic rigidity of the device10 is therefore increased.

The control chamber 50 may be selectively connected to a tank 39 or viaa control line 52 to a pressure source. In the illustrated embodiment,the pressure medium pump 38 of the pressure medium supply device 37serves as a pressure source. It is however likewise conceivable to usesome other pressure source, for example the pressure medium pump 38 of aservo consumer, for example the servo steering system. In said case, thepressure medium flowing out of the control chamber 50 is conducted notinto the tank 39 of the lubricating oil circuit of the internalcombustion engine 1 but rather to the corresponding tank 39 of the servoconsumer.

A further check valve 42 b is provided in the control line 52 andprevents a return flow of pressure medium from the control chamber 50 tothe pressure medium supply device 37.

To control the pressure medium flow to and from the control chamber 50and the counterpressure chamber 58, a control means 60 in the form of adirectional valve 53 is provided. The directional valve 53 is designedas a 4/2 directional valve and has a pressure port P₁, two working portsA₁, B₁ and a tank port T₁. The pressure port P₁ is connected to thepressure source, in the illustrated embodiment via the control line 52to the pressure medium supply device 37. The third working port A₁ isconnected to the control chamber 50, the fourth working port B₁ isconnected to the counterpressure chamber 58 and the tank port T₁ isconnected to the tank 39. In a first control position of the directionalvalve 53, the third working port A₁ is connected to the pressure portP₁, while the fourth working port B₁ communicates with the tank portsT₁.

In a second control position of the directional valve 53, the thirdworking port A₁ is connected to the tank port T₁, while the pressureport P₁ communicates with the fourth port B₁.

The control line opens out into the control chamber 50 via a second port56 downstream of the directional valve 53. Furthermore, a connectingline 55 is provided which connects the control line 52 to the store line51. The connecting line 55 opens out firstly into the store line 51between the check valve 42 c and the first port 56 of the store chamber49, and secondly into the control line 52 between the directional valve53 and the second port 56 of the control chamber 50. A further checkvalve 42 d is arranged in the connecting line 55, which further checkvalve 42 d permits a pressure medium flow from the control line 52 tothe store line 51 and prevents a pressure medium flow in the oppositedirection.

When no adjustment demand is transmitted from the engine controller tothe device 10 during the operation of the internal combustion engine 1,then the control valve 40 is situated in the second (central) positionand the first directional valve 53 is situated in the first position.Consequently, no pressure medium flows to or from the actuating device10 a. A pressure medium flow from the pressure medium supply device 37via the store line 51 to the store chamber 49 is prevented by the checkvalve 42 d. The control chamber 50 is acted on with pressure medium viathe control line 52 and the directional valve 53. At the same time,pressure medium passes via the control line 52, the connecting line 55and the store line 51 into the store chamber 49. At the same time, thecounterpressure chamber 58 is connected to the tank 39 via thedirectional valve 53. The pressure medium introduced into the storechamber 49 or the control chamber 50, respectively, acts on the first orsecond pressure surface 47, 48 respectively, as a result of which thepressure piston 45 is moved in the direction of the stops 54 counter tothe force of the spring element 46, such that the volume both of thecontrol chamber 50 and also of the store chamber 49 increases. At thesame time, the counterpressure chamber 58 is vented into the tank 39.

When a phase angle adjustment is demanded by the engine control unit,the control valve 40 is moved into its first or third position. Pressuremedium therefore passes from the pressure medium pump 38 to the first orsecond pressure chambers 35, 36 respectively, as a result of which aphase adjustment is effected by the actuating device 10 a,b. When thevolume flow fed by the pressure medium pump 38 is too low to ensure theadjustment, or when a higher adjustment speed is to be obtained, thenthe first directional valve 53 is moved into its second controlposition. In said control position, the control chamber 50 is connectedto a tank 39. The pressure medium which is under pressure in the controlchamber 50 is thereby connected to atmospheric pressure, as a result ofwhich a rapid emptying of the control chamber 50 takes place. At thesame time, the store chamber 49 is emptied into the pressure mediumsupply device 37. When the emptying of pressure medium out of thecontrol chamber 50 takes place so quickly that the pressure piston 45 issupported solely by means of the first pressure surface 47 with respectto the store chamber 49, then the entire force of the spring element 46acts only on the store chamber 49. The pressure p in the store chamber49 at the start of the emptying process can therefore be defined asfollows:

$p = \frac{p_{sys}( {A_{1} + A_{2}} )}{A_{1}}$

plus the pressure which is generated by the filling of thecounterpressure chamber 58. This applies when the pressure piston 45 hasnot yet been fully deflected, that is to say is not bearing against thestops 54. Here, p_(sys) corresponds to the system pressure of thepressure medium supply device 37 which prevailed at the start of theemptying of the pressure accumulator 43.

Since the check valve 42 a is arranged in the pressure medium line 41upstream of the store line 51, it is ensured that the entire pressure pand the entire volume of the store chamber 49 is available to theactuating device 10 a, and does not flow out into the oil gallery of theinternal combustion engine 1. Therefore, not only is the present systempressure available, as is the case in applications with conventionalpressure accumulators, but rather a pressure increased by the factor1+A₂/A₁ is available.

Pressure medium is additionally conducted by the control line 52 intothe counterpressure chamber 58. Said pressure medium loads thecounterpressure surface 59 of the pressure piston 45 with a force whichacts in the same direction as that of the spring element 46. Thepressure in the store chamber 49 is additionally increased in this way.

The pressure medium supply device 37 can therefore be provided withpressure assistance, which exceeds that of the conventional pressureaccumulator, by setting the second control position in the firstdirectional valve 53. It is thus possible for the adjustment speed ofthe actuating device 10 a to be significantly increased for the samedimensioning, or for the actuating device 10 a to be designed to besmaller for the same adjustment speed, without having to accept thedisadvantages of an overdimensioned or a regulated pressure medium pump38.

Embodiments are also conceivable in which the connecting line 55 and thearrangement of a check valve 42 c in the store line 53 can be dispensedwith. In operating phases of the internal combustion engine 1 in whichthe phase position is held constant, the pressure accumulator 43 isfilled via the store chamber 51 and the control line 52.

When the system pressure falls, then no pressure medium flows out of thecontrol chamber 50. As a result, the volume of the control chamber 50and of the store chamber 49 remains constant despite the pressure dropin the pressure medium supply device 37. Here, the travel x by which thepressure piston 45 has been deflected out of its initial position isdefined as follows:

$x = \frac{p_{m\; {ax}}( {A_{1} + A_{2}} )}{D}$

where A₁ corresponds to the surface area of the first pressure surface47, A₂ corresponds to the surface area of the second pressure surface48, p_(max) corresponds to the maximum system pressure occurring duringthe filling phase, and D corresponds to the spring constant of thespring element 46. Here, the maximum movement travel is limited by thestops 54.

When the directional valve 53 is moved into the second switchingposition, then the pressure p provided by the pressure accumulator 43when the pressure piston 45 is not yet fully deflected can be defined asfollows:

$p = \frac{p_{m\; {ax}}( {A_{1} + A_{2}} )}{A_{1}}$

plus the pressure which is generated by the filling of thecounterpressure chamber 58.

In order to implement the pressure increase, the ratio Q_(D/V) of thepressure medium flow out of the control chamber 50 to the pressuremedium flow out of the store chamber 49 must satisfy the followingrelationship:

$\frac{Q_{D}}{Q_{V}} > \frac{A_{2}}{A_{1}}$

To achieve this, it is provided that the minimum throughflow crosssection A_(D) between the control chamber 50 and the tank 39 satisfiesthe following relationship:

$A_{D} > {\frac{A_{2}}{A_{1}}A_{V}}$

where A_(V) corresponds to the minimum throughflow cross section betweenthe store chamber 49 and the actuating device 10 a, or the actuatingdevice 10 a and the tank 39.

It is likewise conceivable for one or more further actuating devices 10b, 10 c in addition to the first actuating device 10 a to becontrollable by means of the pressure medium supply device 37 viafurther pressure medium lines 41 and further control valves 40. Here,the further actuating device 10 b can likewise profit from the pressureaccumulator 43. For this purpose, the branch which leads to saidactuating device 10 b is situated downstream of the check valve 42 a inthe flow direction.

If the pressure accumulator 43 is to assist only the first actuatingdevice 10 a, then the branch to the further actuating device 10 c shouldbe arranged upstream of the check valve 42 a in the flow direction.

It is likewise conceivable for the check valve 42 a to be arrangeddownstream of the branch to the store line 51. In this case, thepressure peaks are supported between the actuating device 10 a,b and thebranch to the store line 51. The pressure peaks therefore cannot reachthe pressure accumulator 43, as a result of which more rigid torquetransmission by the actuating device 10 a,b is obtained.

It is likewise conceivable for in each case one check valve 42 a to beused in the pressure medium line 41 upstream and downstream of thebranch to the store line 51. Here, rigid torque transmission by means ofthe actuating device 10 a,b is achieved, and the pressure or thepressure medium volume of the store chamber 49 is also prevented frombeing discharged into the oil gallery of the internal combustion engine1.

In a slight modification of the embodiment, the check valve 42 b and/orthe entire pressure medium line 41, in which the check valve 42 a isarranged between the opening-out points of the pressure accumulator 43,could be omitted.

FIG. 4 shows a further embodiment according to the invention of a device10. In said embodiment, the pressure piston 45 of the pressureaccumulator 43 divides the pressure reservoir 44 into a store chamber 49and the counterpressure chamber 58, with no control chamber 50 beingprovided. The store chamber 49 is delimited in the movement direction ofthe pressure piston 45 by the first pressure surface 47 and thecounterpressure chamber 58 is delimited in the movement direction of thepressure piston 45 by the counterpressure surface 59.

The store chamber 49 can be acted on with pressure medium from thepressure medium supply device 37 via the store line 51. Thecounterpressure chamber 58 is connectable to a pressure source via thecontrol line 52. In the illustrated embodiment, the control line opensout into the pressure medium supply device 37.

The control line 52 is therefore connected to the pressure medium pump38 of the internal combustion engine 1. Other pressure sources such asthe pressure medium pump of a servo consumer may alternatively also beused.

A directional valve 53 designed as a 3/2 switching valve is provided inthe control line 51. The directional valve 53 has a pressure port P₁, aworking port B₁ and a tank port T₁. The pressure port P₁ is connected tothe pressure medium pump 38, the working port B₁ is connected to thecounterpressure chamber 58 and the tank port T₁ is connected to the tank39.

In the first control position of the directional valve 53, the workingport B₁ is connected to the tank port T₁, while the pressure port P₁does not communicate with any of the other ports B₁, T₁. If thedirectional valve 53 is situated in said control position, then thecounterpressure chamber 58 is connected to the tank 39.

In the second control position of the directional valve 53, the workingport B₁ is connected to the pressure port P₁, while the tank port T₁does not communicate with any of the other ports B₁, P₁. If thedirectional valve 53 is situated in said control position, then thecounterpressure chamber 58 is acted on with pressure medium by thepressure medium pump 38.

During the filling phases of the pressure accumulator 43, thedirectional valve 53 is situated in the first control position. Pressuremedium is supplied to the store chamber 49. As a result, the pressurepiston 45 is moved counter to the force of the spring element 46. Thevolume of the store chamber 49 increases at the expense of the volume ofthe counterpressure chamber 58.

In the pressure assistance phases, the directional valve is situated inthe second control position. In said position, pressure medium issupplied to the counterpressure chamber 58, which pressure medium actson the counterpressure surface 59. The resulting pressure forceincreases the force exerted by the spring element 46 on the pressurepiston 45. The assistance pressure provided by the pressure accumulator43 from the store chamber 49 is therefore increased.

Embodiments are also conceivable in which the surface area of thecounterpressure surface 59 is greater than the surface area of the firstpressure surface 47. This provides a pressure boost which has a positiveeffect on the pressure value which can be provided.

FIG. 5 illustrates a further embodiment of a device according to theinvention. Said embodiment corresponds substantially to the embodimentillustrated in FIG. 4. In contrast to the embodiment from FIG. 4, ineach case one check valve 42 b,c is arranged in the store line 51 and inthe control line 52. Furthermore, the directional valve is designed as a4/2 directional valve, with the additional working port A₁ beingconnected to the store chamber 49. In the first control position of thedirectional valve 53, the additional working port A₁ is connected to thepressure port P₁. In the second control position of the directionalvalve 53, the working port A₁ does not communicate with any of the otherports B₁, P₁, T₁.

In said embodiment, pressure medium can pass from the pressure mediumpump 38 via the control line 52 and the directional valve 53 into thestore chamber 49 for as long as the directional valve is situated in thefirst control position. At the same time, the counterpressure chamber 58is ventilated to the tank 39.

When the directional valve 53 is situated in the second controlposition, the working port A₁ is closed and the counterpressure chamber58 is acted on with pressure medium by the pressure medium pump 38. Atthe same time, the store chamber 49 is emptied into the pressure mediumsupply device 37.

The check valve 42 c shields the pressure accumulator 43 from pressurepeaks generated in the actuating devices 10 a, b.

In all of the illustrated embodiments, the pressure accumulator 43 opensout into the pressure medium line 41 which connects the pressure mediumpump 38 to the one or more control valves 40. Embodiments are likewiseconceivable in which the one or more pressure accumulators 43 open outinto the pressure medium lines 41 which connect the one or more controlvalves 40 to the actuating devices 10 a,b.

In addition to the use of the pressure accumulator 43 in applicationsfor variably adjusting the control times of an internal combustionengine 1, the pressure accumulator 43 may also be used in other vehicleapplications, for example in switchable cam followers or in applicationsin automatic transmissions.

LIST OF REFERENCE SYMBOLS

-   1 Internal combustion engine-   2 Crankshaft-   3 Piston-   4 Cylinder-   5 Traction mechanism drive-   6 Inlet camshaft-   7 Outlet camshaft-   8 Cam-   9 a Inlet gas exchange valve-   9 b Outlet gas exchange valve-   10 Device-   10 a First actuating device-   10 b Further actuating device-   21 Sprocket-   22 Outer rotor-   22 a Housing-   23 Inner rotor-   24 Side cover-   25 Side cover-   26 Hub element-   27 Vane-   27 a Vane springs-   28 Vane grooves-   29 Circumferential wall-   30 Projection-   31 Fastening element-   32 Cavity-   33 Delimiting wall-   34 a Early stop-   34 b Late stop-   35 First pressure chamber-   36 Second pressure chamber-   37 Pressure medium supply device-   38 Pressure medium pump-   39 Tank-   40 Control valve-   41 Pressure medium line-   42 a Check valve-   42 b Check valve-   42 c Check valve-   42 d Check valve-   43 Pressure accumulator-   44 Pressure reservoir-   45 Pressure piston-   46 Spring element-   47 First pressure surface-   48 Second pressure surface-   49 Store chamber-   50 Control chamber-   51 Store line-   52 Control line-   53 Directional valve-   54 Stop-   55 Connecting line-   56 Port-   58 Counterpressure chamber-   59 Counterpressure surface-   60 Control means-   A First working port-   B Second working port-   P Inlet port-   T Discharge port-   A₁ Third working port-   B₁ Fourth working port-   P₁ Pressure port-   T₁ Tank port

1. A device for variably adjusting control times of gas exchange valvesof an internal combustion engine, comprising: a drive input element; adrive output element; at least one pressure chamber; a pressure mediumsupply device; and at least one pressure accumulator, with it beingpossible for pressure medium to be supplied to or discharged from the atleast one pressure chamber by means of the pressure medium supplydevice, with it being possible for a phase position of the drive outputelement relative to the drive input element to be varied by means of thesupply of pressure medium to or discharge of pressure medium out of thepressure chamber, with the pressure accumulator having a movable elementwhich is provided with a first pressure surface which partially delimitsa store chamber, with the store chamber being connected or beingconnectable to the pressure medium supply device, with a force storeloading the movable element with a force in a direction of an initialposition, and with it being possible by means of a pressurization of thestore chamber for the movable element to be moved counter to the forceof the force store, wherein the movable element has a counterpressuresurface which at least partially delimits a counterpressure chamber,with it being possible by means of the pressurization of thecounterpressure chamber for the movable element to be moved in thedirection of the initial position.
 2. The device of claim 1, wherein themovable element has at least one second pressure surface which partiallydelimits a control chamber, with it being possible by means of anapplication of pressure medium to the control chamber for the movableelement to be moved counter to the force of the force store, and with apressure medium flow within the pressure accumulator from the storechamber into the control chamber being prevented.
 3. The device as claim2, wherein an application of pressure medium to the store chamber movesthe movable element in the same direction as an application of pressuremedium to the control chamber.
 4. The device of claim 1, wherein thecounterpresssure chamber can be selectively connected to a pressuresource or to a tank.
 5. The device of claim 1, wherein control means areprovided, with it being possible for the counterpressure chamber to beselectively connected to a tank or to a pressure source by the controlmeans.
 6. The device of claim 1, wherein the counterpressure chamber canbe connected to a pressure medium pump of the internal combustionengine.
 7. The device of claim 1, wherein the counterpressure chambercan be connected to a tank of the internal combustion engine.
 8. Thedevice of claim 5, wherein a directional valve is provided as a controlmeans, which directional valve has in each case one port connected to apressure source, to a tank and to the counterpressure chamber.
 9. Thedevice of claim 8, wherein the directional valve has a further portwhich is connected to the store chamber or to a control chamber.
 10. Thedevice of claim 2, wherein the store chamber and the control chamber donot communicate with one another within the pressure accumulator.